Liquid dispensers for dispensing soaps and other similar fluids in liquid form are known. For various reasons in some applications, it is preferable to dispense soaps and other similar fluids in the form of a foam. Generally, in the form of a foam, less soap liquid is required to be used as contrasted with the soap in the liquid form. As well, soap as foam is less likely to run off a user's hands or other surfaces to be cleaned.
Known liquid dispensers for dispensing foams include the dispenser taught by U.S. Pat. No. 5,445,288 to Banks, issued Jul. 29, 1995. A disadvantage which the present inventor has appreciated with dispensers such as those taught by Banks is that when used with a non-collapsible or rigid sealed container of soap liquid, a vacuum comes to be developed in the container which renders the dispenser inoperative.
Known liquid dispensers for dispensing liquids without foaming of the liquids are also known. The present inventor has also appreciated that many such dispensers also suffer the disadvantage that they are not suitable for use with non-collapsible or rigid sealed containers since the pumps develop a vacuum in the container. Non-collapsible or rigid sealed containers have the disadvantage of requiring various one-way valve mechanisms to permit air to enter the containers under vacuum to equalize the pressure in the containers with atmospheric pressure. Such one-way valves typically suffer the disadvantage that they maintain at least some vacuum pressure differential in the container and with many viscous soaps, the presence of even a slight vacuum can negatively affect dispensing.
The present inventor has also appreciated that known soap dispensers suffer the disadvantage that they do not permit for positive replacement of air for liquid dispensed from a liquid reservoir and/or do not permit a positive pressure to develop in a container.